1. Field of the Invention
The invention relates to a process for preparing equilibrated organopolysiloxane mixtures with organosulfonic acid groups linked to silicon by reacting organosiloxane compounds with organosulfonic acids or organodisulfonic acids.
2. Description of the Prior Art
Organopolysiloxanes with terminal reactive groups play an important industrial role. Such siloxanes, which were equilibrated by incorporating sulfate groups, are particularly important. As used herein, equilibration is understood to mean the equilibration of the polysiloxane mixture with regard to the molecular weight distribution and the distribution of possible different organosiloxane units within the molecule. At the same time, the sulfate groups can also take on the function of a terminal reactive group. An extensive patent literature deals with this subject and the German Pat. Nos. 2,059,546 and 2,059,554 are representative of this literature.
German Pat. No. 2,059,546 relates to a process for preparing predominantly linear, equilibrated organopolysiloxane mixtures with terminal sulfuric acid groups having the general formula ##STR1## wherein N = 2 TO 20, AND R is a hydrocarbon residue which optionally may be substituted with a residue which is inert towards sulfuric acid and in which a part of the hydrocarbon residue R can be replaced by the ##STR2## residue which is in equilibrium with sulfuric acid and cyclic compounds of the general formula ##STR3## wherein R has the same meaning as before and, in each case, two of the ##STR4## residues can be replaced by a ##STR5## RESIDUE; M = 1 TO 10 AND PREFERABLY IS 1 OR 2.
German Pat. No. 2,059,554 relates to a process for preparing equilibrated mixtures of polydiorganosiloxanyl sulfates of the general formula ##STR6## The substituents and indices in the above formulas have the following meaning:
n = 2 to 20 and preferably is 2 to 10,
m = 1 to 10 and preferably is 1 to 2,
R represents the same or different low molecular weight, optionally substituted alkyl residues with preferably 1 or 2 carbon atoms, which may be replaced partially by aromatic residues, preferably a phenyl residue, or by the residue ##STR7## or in which, in each case, two R residues are replaced intermolecularly or intramolecularly by a residue having the structure ##STR8##
Organopolysiloxanes which also have terminal silyl halide, especially silyl chloride, groups, in addition to siloxanyl sulfate groups, are especially interesting. The preparation of such compounds is described, for example, in German Pat. No. 1,174,509 as well as in U.S. Pat. No. 3,115,512. The siloxanyl sulfate groups ensure a rapid development of the equilibrium state.
The above-mentioned compounds find much use as starting materials, for example, for the preparation of polysiloxanes with terminal hydroxyl groups or of polyalkylsilicic esters, of polysiloxanes with acyloxy groups, or they are used for modifying, for example, epoxide resins.
The reactions with high molecular weight hydroxyl compounds for the preparation of polysiloxane/polyoxyalkylene block compolymers, such as are described, for example, in the previously mentioned U.S. Pat. No. 3,115,512, have become particularly interesting. These reactions tend to be accompanied by side reactions which originate from the reaction of liberated sulfuric acid with organic hydroxyl compounds and result in the formation of sulfuric acid esters. Although these side reactions can be suppressed by the use of acid acceptors, there are some cases in which small amounts of by-products nevertheless separate out.
It is an object of German Pat. No. 2,331,677 to find reactive groups which can take over the role of the intramolecular or terminal sulfate groups which, in each case, are linked to one or more silicon atoms without having the disadvantages of these sulfate groups. These reactive groups must have a similar equilibrating effect as siloxanyl sulfate groups without, however, giving rise to interfering side reactions.
This object was accomplished by reacting organohalogen silanes or silane mixtures with an amount of water which was insufficient for splitting off all of the halide residues, and an organosulfonic acid in amounts of 0.005 to 1 equivalents/mole of silane.
This process has proven its value in practice. Nevertheless, it has some disadvantages. For example, organohalogen silanes are required as the raw material for carrying out the process. These silanes are corrosive and dangerously flammable substances. In addition, appreciable quantities of hydrogen halides are formed. Since these materials are acids, highly corrosion resistant installations must be used and considerable efforts must be made in order to remove them to avoid harmful effects on the environment. In addition, there exists the danger that the escaping hydrogen halide entrains silanes from the reaction, so that the control of the adjustment of the molecular weight of the reactive organopolysiloxane becomes more difficult.